How do you reset to retry the current level/room?
From the Manual:
You cannot reset the current room (ie. the room that the player is in).
Make the game save automatically when the player enters a room, with e.g. SaveGameSlot.
For retrying, use RestoreGameSlot with the same int.
If it's just for a single room:
When you create a room, the "Create New Room" window has a checkbox which asks you whether to reset the room once the player has left. Click that.
The room number will then be 300 + (room number)